The present invention relates to an electrical-hydraulic fluid power converter. More specifically, the present invention relates to a device that includes an electric machine coupled to a hydraulic machine.
In material handling and other related fields, lift trucks are often used for transporting heavy materials. Such trucks often use a large lead acid storage battery or similar device as a source of electrical power. Lift trucks also typically use a system of hydraulic cylinders for the purpose of raising, lowering, tilting, reaching, shifting, and other load manipulation functions. With conventional trucks, it is common to use a battery powered electric motor to turn a hydraulic pump. With this system, hydraulic pressure and flow are produced by the pump and are modulated through a system of valves that are fluidly connected to a series of hydraulic cylinders for moving the payload.
In the prior art, the use of various direct current electric motors is well known. Recent developments in the art of solid state power electronics have enabled the use of alternating current (AC) motors to perform various functions within industrial trucks. Such AC motors and their solid state controls provide several advantages in industrial trucks which are well known in the art.
Additionally, the use of electric motor coupled with a hydraulic pump is well known in the art. An example of a prior art electro-hydraulic power converter is disclosed by U.S. Pat. No. 5,591,013 to Kawafune et al. The Kawafune et al. patent, as well as the prior art cited therein, discloses a swash plate type axial piston pump disposed within the center of the rotor of an electric motor. Advantages and disadvantages of this design are apparent to persons skilled in the art.
The present invention improves on Kawafune et al. by teaching a device which places a rotary cam type hydraulic machine, such as a hydraulic piston unit or more specifically a pump, adjacent to and within the same housing as the electric machine. To further improve upon Kawafune et al., a rotary cam type piston hydraulic power unit is used. The best known forms of rotary cam type hydraulic power machines are the wobble plate pump and the radial piston pump. Other variations of the rotary cam hydraulic power units could optionally be used in the present invention.
The present invention seeks to build upon recent developments in the field of electric motors and related components for battery powered industrial trucks. The present invention accomplishes this goal by teaching an electro-hydraulic power converter with a rotary cam hydraulic power unit that improves efficiency, lowers cost, reduces size, simplifies installation, and increases reliability.
It is therefore a primary object of the present invention to teach an electro-hydraulic power converter including a rotary cam hydraulic power unit that has improved efficiency, reduced cost, decreased size, simplified installation, and improved reliability.
It is yet another object of the present invention to provide such a unit where the housing is flooded with hydraulic fluid to provide cooling and lubrication to the electric motor and pump components.
Still another object of the present invention is to provide an integrated unit which incorporates power electronics to control the operation of the electric motor. These controls may optionally take the form of a three phase AC inverter.
Another object of the present invention is to provide a unit which optionally incorporates solenoid or other valves within the unit for the purpose of controlling and adjusting the performance of the hydraulic loads that are powered by the unit.
Still a further object of the present invention is to provide a unit where individual power unit cylinders or clusters of power unit cylinders are assigned to specific functions of a vehicle. For instance, if the unit has nine cylinders total, six cylinders may be connected to provide hydraulic fluid to the main lift cylinder of the industrial truck and the remaining three cylinders may be used to provide flow to the tilt, shift, reach, grab, steering or other auxiliary functions of the vehicle.
These and other objects will be apparent to those skilled in the art.